1. Field of the Invention:
The present invention relates to a two-wheel drive cycle, i.e. a bicycle or motorcycle, comprising a power train capable of driving the front wheel substantially as efficiently as the rear wheel.
2. Brief Description of the Prior Art:
A prior art two-wheel drive bicycle is disclosed in International patent application published under number WO 91/12167 (Biannic et al.) on Aug. 22, 1991.
This bicycle comprises a rear wheel driven through the conventional pedals, cranks, chain wheel, chain and sprocket cluster. An additional sprocket is mounted on the rear wheel to drive the front wheel through first and second chains. The first chain is meshed with the additional sprocket of the rear wheel while the second chain is meshed with a sprocket mounted on the front wheel.
To enable easy steering of the front fork assembly, on which the front wheel rotates, the first and second chains are interconnected through a cardan joint mounted on the pivotal connection between the fork assembly and the frame of the bicycle, that is on the head tube of that frame.
The two-wheel drive bicycle of International patent application WO 91/12167 presents the following drawbacks:
the head tube of the frame as well as the fork assembly must be cast and/or machined to receive the cardan joint;
a cardan joint is complex and additional pieces such as bushings, needle bearings, etc. are required upon installation; it is therefore very expensive;
in the cardan joint used in International patent application WO 91/12167, the rotational speeds of the input and output shafts are different during two angular portions of each revolution;
the major disadvantage is that the different pieces of the cardan joint and those necessary to its installation withstand important stresses and therefore produce a lot of frictional losses; these losses obviously require an additional effort from the cyclist, which effort is not used to drive the bicycle; and
all the pieces of the cardan joint requires specialized maintenance as well as frequent lubrication.
The present inventor has constructed a two-wheel drive bicycle using a cardan joint as disclosed in the aforementioned International patent application, and obtained poor results due to the above mentioned drawbacks related to the use of a cardan joint.